Currently most of the world's commercially available solar thermal electric power is by systems using parabolic trough solar collectors. Another approach is the central receiver or power tower technology. This is based on the concept of many flat two-axis sun tracking mirrors (heliostats) that reflect the beam radiation to a common focal zone. The focal zone is placed well above the heliostat field, on a central tower. This is to help prevent interference between the reflected radiation and the other heliostats. A solar receivers array at the focal zone absorbs the concentrated radiation, converting it to heat. However, these systems are all Rankine steam cycles converting the delivered solar thermal energy with a maximum efficiency of 30 to 39%. Today modern gas turbine systems achieve efficiencies between 40 and 58% when operated in single cycle or as combined cycle plants. Combining solar energy and gas turbine technologies allows conversion of the solar energy into electricity at substantially increased efficiency as compared with the parabolic trough system. In turn, as the collector field is the major part of the solar system investment, it allows for the reduction of the solar collector area by the same amount to achieve a given solar share. The result is a substantial cost reduction of solar electricity.
Adapting a gas turbine to high temperature solar receivers and solar tower technology constitutes genuine progress towards commercial solar power utilization with high efficiency in the combined cycle power system. Solar gas turbine systems can also be adapted to hybrid solar/fossil fuel operation, due to its high efficiency conversion, relatively small solar field, quick response to load fluctuations, low CO2 emissions and more effective equipment utilization.
With respect to prior art solar towers having a height in the order of 100 m, a plurality of heliostats acting as solar collectors automatically track sunlight and concentrate the solar radiation onto a central receiver at the top of a tower to power a turbine.
Air is one medium that is used to extract the concentrated solar energy from the central receiver. In an open Brayton Cycle, air is compressed by the compressor to increase its pressure. The compressed air is delivered to the central receiver and heated to a high temperature. This hot air is then passed from the central receiver to the turbine where it expands, causing the turbine rotation, driving the generator to produce electricity as well as the compressor to compress the supplied air. The air exiting the turbine is exhausted to the surrounding ambient air.
The compressor, turbine and generator used in conjunction with the Brayton Cycle are all mounted on top of the tower. Since these components are especially heavy, the capacity of the power plant has to be limited to lower the weight of compressor, turbine and generator mounted on top of the tower, thereby ensuring structural integrity of the tower. Alternatively the solar tower would have to be immense and expensive to manufacture and assemble if a large sized compressor and turbogenerator were mounted on the tower.
The present invention advantageously provides a power plant comprising of a Brayton cycle associated with a solar tower superior to that of the prior art.
Furthermore, the present invention advantageously provides a Brayton cycle power plant which is less sensitive to intermittent cloudiness. Additionally, the present invention provides a power plant based on a solar tower that is cost effective and economical by using lighter and cheaper such as wind power plant type towers.
Other advantages of the invention will become apparent as the description proceeds.